MemTest86 is a free, thorough, stand alone memory test for x86 architecture computers.
There are many good approaches for testing memory. However, many tests simply throw some patterns at memory without much thought or knowledge of memory architecture or how errors can best be detected. This works fine for hard memory failures but does little to find intermittent errors. BIOS based memory tests are useless for finding intermittent memory errors.
RAM chips consist of a large array of tightly packed memory cells, one for each bit of data. The vast majority of the intermittent failures are a result of interaction between these memory cells. Often writing a memory cell can cause one of the adjacent cells to be written with the same data. An effective memory test attempts to test for this condition. Therefore, an ideal strategy for testing memory would be the following:
It should be obvious that this strategy requires an exact knowledge of how the memory cells are laid out on the chip. In addition there are a never ending number of possible chip layouts for different chip types and manufacturers making this strategy impractical. However, there are testing algorithms that can approximate this ideal and MemTest86 does just this.
MemTest86 was originally developed by Chris Brady with a first release in 1994. However, some of the testing algorithms used have been under development since 1981 and have been previously implemented on Dec PDP-11, VAX-11/780 and Cray XMP architectures. Since then there has been more than a dozen new versions being released. Support for 64bit, new CPU types, symmetrical multiprocessors and many other features have been added during this period. In Feb 2013, PassMark Software took over the maintenance of the project from Chris. We have created a support forum where users can discuss issues. The MemTest86 v4 project remains open source.
Starting from MemTest86 v5, the code was re-written to support booting from the newer UEFI platform. UEFI is able to provide additional services that is unavailable in BIOS, such as graphical, mouse and file system support. The software (Free Edition) still remains free to use without restrictions. For advanced/enthusiast users or commercial applications, a professional version is available for users that require additional customizability and advanced features that may be more suitable for their testing needs. A comparison of the different versions can be found here
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